Strain insulator



Dec. 13, 1966 J. o. SWEENY ET Al.

STRAIN INSULATOR Filed July 50. 1965 United States Patent Office 3,291,890 STRAIN INSULATOR James 0. Sweeny, Pittsfield, Mass., and Norman F. Walters, Baltimore, Md., assignors to General Electric Company, a corporation of NewYork Filed July 30, 1965, Ser. No. 475,917 Claims. (Cl. 174-30) This invention relates to electrical insulators for bearing mechanical strain. or tension and more particularly to improvements in insulators for guying radio towers and supporting antennas, especially in the very low frequency range.

Such insulators should be as light as possible and as small as possible for any given voltage rating so as to minimize gravity loading and windage loading of the tower or antenna.

In accordance with this invention, there is provided a novel insulator construction which has high electrical strength with relatively small size and weight by attaching two similar hollow half insulators together and then filling the cavity space therein with a high electrical strength light weight fluid such as compressed gas.

An object of the invention is to provide a new and improved electrical insulator.

Another object of the invention is to provide a strain insulator having a high ratio of electrical strength to projected area and weight.

A further object of the invention is to provid'e a novel and simple insulator for guying radio towers and supporting antennas.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing,

FIG. 1 is a side elevation view partly in section of a preferred embodiment of the invention, and

FIG. 2 is a sectional View thereof taken on line 2-2 of FIG. 1.

Referring now the the drawing and more particularly to FIG. 1, the insulator comprises similar or substantially duplicate half insulators 1. Inasmuch as their constructions are similar and the upper one as viewed in the drawing is shown partly in section only this one will be described in full detaiLit being understood that the other or lower one as viewed in the drawing is essentially the same. It comprises a hollow metal frame 2 of any suitable material such as high strength steel and as indicated in FIG. 2 it is preferably of circular cross section. It may either by cylindrical as shown or frustoconical or any other suitable surface of revolution, and it is provided with an outwardly extending flange 3 at one end and an inwardly extending shoulder 4 at the other end. Seated 4on and preferably cemented to the inner surface of the shoulder 4 is an electrical insulating member 5 of any suitable configuration such as frustoconical as shown. It should be strong in compression and may be made of electrical grade porcelain. Similarly seated on and preferably sealed to the outer surface of the shoulder 4 is an outer insulating member 6 which is substantially longer in the axial direction than the insulator 5 and which is preferably provided with so-called petticoats for increasing its outer surface electrical creepage distance. It is also shown of frustoconical shape and may similarly be made of electrical grade porcelain.

For hermetically sealing the joints in the half unit, a cap 7 preferably of metal such as steel cemented to the other end of the inner insulating member 5 which cap is internally threaded and a cap 8 of suitable material such as comparatively thin sheet metal is seated on the outer end of the insulating member 6. A pipe 9 of suitable 3,291,890 Patented Dec. 13, 1966 material such as steel is threaded into the cap 7 and extends into'the cap 8 and carries a nut 10 threaded to that end. Below the nut 10 is a sliding washer 11 between which and the bottom of the cap 8 is a compression spring 12. The washer 11 is pressed down and the spring 12 compressed by means of a set screw or screws 13 threaded into the nut 10. Gaskets 14 are provided at the ends of the insulating member 6 and additional porcelain to metal seals 1S are provided between the member 6 and the shoulder 4 on the one hand and the cap 8 on the other hand so as to insurean hermetic seal. In this manner, the insulating member 6 is maintained under substantial compression regardless of whether or not there is a working load on the insulator.

Passing through the pipe 9 is the shank 16 of an eyebolt whose eye 17 is at the outer end and whose inner end is threaded and carries a nut 18 which bears against the cap 7. In this manner, insulator strains are transmitted through the tensioned eyebolt for applying compressive force to the insulating member 5. The outer end of the half unit is sealed by a complementary cap portion 19 of suitable material which is brazed to the shank 16 of the eyebolt and the rim of the cap 8. The material of the cap 19 is comparatively weak mechanically and flexible so that any minor elongation of the eyebolt will not materially affect the compressive force on the outer insulating member 6.

A hole 20 is provided in the cap 7 for providing a communicating passageway between the inner space between the pipe 9 and the insulating members 5 and 6 and the outer space or cavity in the frame 2.

The two halves of the insulator are fastened together at their flanges 3 by through bolts 21, the joint preferably being sealed by a gasket 22 and a brazed seal 23. Each frame 2 may also be provided with a sheet metal half shield 24 of smooth contour brazed thereto as at 25 and the adjoining rims of these shields 24 may be sealed by brazing as at 26.

The insulator is filled through a filling plug 27 with an insulating fluid such as light weight compressed high insulating strength gas, a preferred gas being sulphur hexafluoride.

In order to shield the comparatively sharp edges of the nuts 18 so as to reduce the electrical stress concentrations in the insulating fluid, these nuts are preferably covered by smooth contoured thin metal caps 28.

In operation, the insulator is of course connected at its end eyes 17 in a guy wire so that it transmits the strain in the guy wire and at the same time electrically insulates or isolates the two sides of the guy wire which are connected to the ends of the insulator.

By reason of the high electrical strength of the fluid filling the interior spaces of the insulator, the electrical clearance distance therein may be made much shorter than the similar distances on the outside of the insulator in the open air so that, for example, the length of the internal insulator 5 and the strike distance between the caps 28 can be comparatively small thus permitting a substantial reduction in size and weight of the entire insulator.

By means of the above described construction, the insulator will have twice the electrical strength of either of its halves alone while still having the full mechanical strength of either of its two halves While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

wardly extending ange at one end and an inwardly extending shoulder at the other end, an `eyebolt extending on the outer side of said shoulder, a metal shell surrounding said eyebolt adjacent the eye thereof and sealingly attached thereto and to the other end of said second insulating member, a tension bearing pipe surrounding the shank t of said eyebolt, said pipe being threaded into said cap and extending into said shell, means in said shell connected to the end of said pipe which-is in-said shell for applying a compressive force to saidinsulating members which is independent of the working strain on said inf 25 so that said frame members extend in opposite directionssulator; means sealingly attaching said anges together and an insulating fluid filling the spaces in said insulator.

2. A strain insulator comprising, in combination, duplicate halves each having: a hollow cylindrical steel frame g with an outwardly extending ange at one end and an inwardly extending shoulder at the vother end, a steel eyebolt extending into said frame through its shoulder and terminating in a threaded end in said frame near its ange,

in combination dupli- .l cate halves each having: a hollow frame with an out a nut on the threaded end of said eyebolt, a frustoconical 1,

compression bearing porcelain insulating member sur-4 rounding the threaded end of said eyebolt and' seated at one end on the inner side of said shoulder, a steel cap surrounding the theaded end of saideyebolt between said nut and the lother end of said compression bearing pome lain insulating member, a second frustoconical porcelain insulating member surrounding said eyebolt and seated at one end on the outer side of said shoulder, a metal shell surrounding said eyebolt adjacent the ,eyey thereof and sealingly attached thereto and to the other end of said secondA frustoconical insulating member, a tension bearing pipe surrounding the shank of said eyebolt, said pipe being threaded into said cap and extending into said shell, means in said shell connected to the end of said' pipe which is in said shell for applying a resilient compressive force to said means sealingly attaching said ilanges together so that said frame members extend in opposite directions, and a compressed insulating gas filling the spaces in said insulator. g i

l 3. An' insulator as in claim 2 in which said gas is sulphur hexafluoride.

4. An insulator as in claim 1 in which the` insulating members whichare Aseated onvthe inner surface of a shoulder are substantially shorter in length and still shorter in surface creepage'distance than'the insulating members which are seated on the outer surface of a shoulder, a smooth contouredmetal cup shell covering each nut and an opening through each cap whereby said uid has access to the space between each pipe and the insulating members surroundingitp 5.1A'strain insulator comprisingin combination, simi lar halveseach having: a hollow metal frame with a coupling end and an inwardly extending shoulder at the other e-nd, an eyebolt extendingfintosaid frame through its shoulder end and having an enlarged end in said frame and an eye end outside said frame, -v'insulating members surrounding said eyeboltfand seatedLv respectively on the inner, and outer surfaces of saidj shoulder, said enlarged end of-said eyebolt serving tof-"convert a tension force lon lsaid eyebolt to -a compressive forcel in the insulating member which is seated onthe inner surface of said shoulder, spring means independent of'said eyebolt pressing said insulatingmemb'ers against said surfaces; mea-ns sealingly fastening said couplingrendstogether in'facfe yto face relation, and an insulatingtlluidhaving a higher dielectric strength than -air lli-ng'the remaining spaces in said insulator and being in contact with'both sides of the insulating vrrier'nbers which are seated on the inner surface lof said shoulders.

References Cited by the Examiner UNITED STATES PATENTS v904,069 11/1908 Kempton 17a-181x 937,896 10/1909 Varney etal 174-181 X 11,080,713- 12/1913 Mead et a1. 174-178 FOREIGN PATENTS 2/ 1946 Switzerland.

LARAMIE E. ASKIN, Primary Examiner, 

5. A STRAIN INSULATOR COMPRISING, IN COMBINATION, SIMILA HALVES EACH HAVING: A HOLLOW METAL FRAME WITH A COUPLING END AND AN INWARDLY EXTENDING SHOULDER AT THE OTHER END, AN EYEBOLT EXTENDING INTO SAID FRAME THROUGH ITS SHOULDER END AND HAVING AN ENLARGED END IN SAID FRAME AND AN EYE END OUTSIDE SAID FRAME, INSULATING MEMBERS SURROUNDING SAID EYEBOLT AND SEATED RESPECTIVELY ON THE INNER AND OUTER SURFACES OF SAID SHOULDER, SAID ENLARGED END OF SAID EYEBOLT SERVING OF SAID SHOULDER, SAID ENLARGED ON SAID EYEBOLT TO A COMPRESSIVE FORCE IN THE INSULATING MEMBER WHICH IS SEATED ON THE INNER SURFACE OF SAID SHOULDER, SPRING MEANS INDEPENDENT OF SAID EYEBOLT PRESSING SAID INSULATING MEMBERS AGAINST SAID SURFACES; MEANS SEALINGLY FASTENING SAID COUPLING ENDS TOGETHER IN FACE TO FACE RELATION, AND AN INSULATING FLUID HAVING A HIGHER DIELECTRIC STRENGTH THAN AIR FILLING THE REMAINING SPACES IN SAID INSULATOR AND BEING IN CONTACT WITH BOTH SIDES OF THE INSULATING MEMBERS WHICH ARE SEATED ON THE INNER SURFACE OF SAID SHOULDERS. 